Process for removing chlorine from zinc sulphate solutions



Patented 21, 19133 325 WILLIANZ J. OBBIEN, OF CLEVELAND, QEIO, ANDJOSEPH E. BEAPEAU, J11, OF NEW YORK, N. Y., ASSIGNGBS TO THE GLIDDENCOMPANY, Q}? CLEVELAIQD, OHIO, A COB- J'PGEATION OF 0310 I PROCESS FURREMOVING CHLORINE FROM ZENC SULPHATE SOLUTIOlTS i No Drawing.Application filed May 8, 1931. Serial No. 535,570. In a process for themanufacture of litho- Chile by C. VI. EichrodtA. l. M. E. pone, thechlorine content of the zinc sul- 1930 Transactions. phate solutionplays a very important part. 2. The Hunt and Douglas Process copper Chloe down to one part per million of dissolution as sulphate andprecipitachlor per liter of Zinc sulphate solution tion as insoluble CuC1 as described in 35 Beauin Fahrenheit will affect ap- Transactions A.l. M. Vols. X and preciably the photogenic properti s of litho- XVI.

pone. Attention is called to the literature The authors in studyingvarious references on the manufacture of lithopone and to the and theliterature on this subject, have 10 following patents: found in no casehas a practical or 60 Breyer, Croll 8*- Farherll. S. Patent No.economical solution of the problem been obl, lll. 6 l5lssued April 4-,1922 tained and that decided improvements over Singinaster BreyerU. S.Patent No. the present at would have to be made be- 1 ll.1 .648lssuedApril l, 1922 the process of removing chlorides from zinc 15 SinginasterBreyer-U. S. Patent No. sulphate solutions would be economically 5"1,lll,64s7-lssued April ll, 1922 sound. Singniaster Breyer- U. S. PatentNo. Citing some of the ditliculties in thevaril, l1l,6 l8lssued April4-, 1922 one proposed methods, We might mention Breyer 6?: F1Tb81U. S.Patent No. L446,- the presence of arsenic which generally 00- 7 2e637lssued Feh. 27, 1923 curs in zinc sulphate solutions, particularly inSingniaster 8; Breyer-U. S. Patent NO. zinc sulphate solutions made fromzinc bear- 1ll l,793lssued May 2, 1922. fumes. The authors have foundthat if Chlorine in zinc sulphate solutions used the right conditionsare obtained, one pound for electrolytic Zinc also is an objectionableof copper will precipitate one pound of chlofeature because of EuJiIlQlosses, etc. he rine as cuprous chloride. However, in the part chlorineplays in lithopon inanufacpresence of arsenic unless the properconditure and in electrolytic zinc is so important tions ofprecipitation are used the arsenic that lithopone manufacture s will notuse will go down with the copper as insoluble Zinc materials containingover 5% chlorii c. cop oer compounds and the consumption of 20 .Llso,electr lytic zinc m nufacturers are copper will greatly increase thecost for the faced with the problem 0 the disposal of removal ofchlorine. Iron, which is always their dross containing from 2% to 0present in zinc sulphate solutions in varying This dross is isby-product requantities also interferes with this reaction where theyand unless the operation is carried on under 35 the anode. the properconditions the iron will precipiaware that a great deal tate with thecopper, interfering; with the been done in the on the resubsequentregeneration of the copper. moral of chlorine from both copper sulphateIt wa also found in this experimental ZlllC sulphate. oin copper su workthat the more nearly neutral or basic a solution was the more colloidaland slimy the copper chloride precipitate. lhe au- 3 found practicallyimpossible to filter or e the resulting cuprous chloride unless specialconditions were usedin the treatin c5 I Laist U. S. Patent No. l 'lOl,9O7ls Cuill Cu=Cu Cl must be carried on sued July 28, 19A in an acidreaction. They found that the and the following references: opti nuincondition for precipitatlon of the 59 l. The Leaching Process atChuquicaniata cuprous chloride, is that the zinc sulphate solution mustcontain between 2% and 1.5% free sulphuric acid depending upon theimpurities present. For example, if the Zinc sulphate solution is low inarsenic and iron, 2% of free sulphuric acid is permissible and will worksatisfactorily.

The authors have also found that under the conditions of the process,the reaction CuCl +Cl is endothermic and therefore should be carried outin hot solutions.

The process of removing chloride from zinc sulphate, therefore, differsfrom the methods already described in the literature by maintaining adefinite acid condition and a certain temperature. Our process is asfollows:

Zinc sulphate from approximately 35 Beaum at 60 Fahrenheit, containingvarying amounts of impurities which usually occur with impure zincsulphate, such as ar-- senic, iron, manganese, tin, copper, chlorine,etc., is run into a large treating tank and heated to a temperatureranging from 140 to 200 Fahrenheit. The acidity of the Zinc sulphatesolution is brought to the proper amount, varying between 2% and 1.5%,depending upon the amount of impurities, particularly iron and arsenic.It is preferred to operate at the minimum acid content to lessensubsequent steps in the operation. The amount of acid used is alsoaffected by the colloidal and slimy nature of the cuprous chloride,which in turn is afl'ected by the varying amounts of impurities,particularly tin. Sufficient acid should be present so as to produce thenecessary coagulating effect on the cuprous chloride and prevent thecoprecipit-ation of the arsenic. iron, and possibly tin, and prevent theoxidation of colloidal oxide if tin should be present.

To the zinc sulphate solution described above, is added sufiicientcopper sulphate to combine with the chlorine present so that chlorineexisting in the zinc sulphate solution exists in the presence ofsufiicient copper as copper sulphate to combine with it.

To the zinc sulphate solution containing copper sulphate solution is nowadded sutiicient copper powder to convert the chlorine -to insolublecuprous chloride.

' bring the acidity of the zinc sulphate solu-

